The synthesis of metallic nanoparticles inside live plants

There is increasing commercial demand for nanoparticles because of their wide applicability in a growing number of fields, e.g. electronics, catalysis, chemistry, energy, and medicine. Metallic nanoparticles are traditionally synthesized by wet chemical techniques, where the chemicals used are quite often toxic and flammable. In this work, we describe a cost effective and environmentally sound technique for the synthesis of metallic nanoparticles using live plants. We have adopted the generic term, phytosynthesis to describe this process. Nanoparticles of common heavy metal ions, e.g. Ag, Cu, Co, Zn and Ni, were synthesized by exposing plants to aqueous metal salt solutions. These experiments were used to evaluate the potential of two known hyperaccumulator species Brassica juncea, Helianthus annus and Medicago sativa for producing nanoparticles. The influence of exposure time, substrate metal ion concentration and chelating agent addition were all investigated. Brassica juncea was found to be the best plant for sequestering metals from aqueous solutions and depositing them as intracellular nanoparticles. Metal concentrations were determined by atomic absorption and inductively coupled plasma spectroscopy. Transmission electron microscopy was used to measure the size and shape of the nanoparticles formed.